1. Technical Field
The invention, in its several embodiments, pertains to optical devices, systems, and processes for simulating the optical transmission of living tissue, and the present field of endeavor more particularly pertains to light transmission simulators and processes of living tissue for pulse oximeters.
2. State of the Art
Oximeters may be used for measuring the blood saturation oxygen level (SpO2) of living tissue, for example, that of a patient in a diagnostic environment. Typically, the patient inserts a digit into a receiving portion of the oximeter.
Living tissue simulators may include a photodiode and a light emitting source. The simulating unit is configured such that when it is inserted into the sensor of the target oximeter, its photodiode is aligned in opposition with the light emitting diode (LED) of the target oximeter, while its light emitting source is aligned in opposition with the photo detector in the sensor of the target oximeter. The simulating unit may be connected to a simulator main module which can include a comparator circuit, a digital to analog circuit, a light emitter driver circuit, and a processor circuit.
Pulse oximeters detect the oxygenation of arterial blood by using the differential absorption of hemoglobin by red and infa-red light. A pulse oximeter may alternately illuminate living tissue (e.g., one side of a human digit) with alternating flashes of red and infra-red light of constant amplitude and at a repetition rate that is high compared to an expected maximal heartbeat rate. As the heart takes a beat the finger expands and contracts slightly, the optical path length is increased resulting in the attenuation of the light applied to the finger. The attenuated light is captured by a photodetector of the pulse oximter, and thereafter the amplitude modulated light flashes are processed to determine blood oxygen by detecting and processing the red and infa-red heartbeat-modulated signals.
Simulators that may be used to evaluate pulse oximeter performance are often attenuators and amplitude modulators. That is, the pulse oximeter living tissue simulator receives the red and infrared light flashes of the target pulse oximeter and/or their electrical analogues, and attenuates the signals and modulates their amplitudes to generate outputs for the target oximeter similar to the light transmissions of living tissue.